The present application is related to commonly assigned, copending Application No. PCT/US09/33512 entitled METHOD AND APPARATUS FOR NO2-BASED REGENERATION OF DIESEL PARTICULATE FILTERS USING RECIRCULATED NOX, filed on the same date as the present application, and claims the benefit of U.S. Provisional Application 61/063,900, filed Feb. 7, 2009, entitled METHOD FOR MAXIMIZING SOOT REDUCTION CAPACITY OF NO2 REACTANT FOR ACTIVE NO2 REGENERATION OF PARTICULATE FILTER.
The invention relates to methods and apparatus for regeneration of diesel particulate filters (DPFs), that is, removal of accumulated particulate matter or soot from the DPF, and more particularly to methods and apparatus involving an oxidation reaction with NO2.
The most common method for removal of soot from a DPF is oxidation of the trapped soot to produce gaseous products (CO2 and CO) which can pass through the filter media; this process is referred to as regeneration. There are two primary mechanisms employed for regeneration: oxidation of soot by O2 ((C+O2→CO2) and/or (2C+O2→2CO)) called O2-based regeneration and oxidation of soot by NO2 ((C+2NO2→CO2+2NO) and/or (C+NO2→CO+NO)) called NO2-based regeneration.
Presently known and implemented solutions for DPF regeneration comprise active O2-based regeneration systems, passive NO2-based regeneration systems, or a combination thereof. Active O2-based regeneration systems raise the temperature of the reactants, through a variety of methods, in order to establish and sustain an O2/soot reaction. During active O2-based regenerations, substantially all soot removal is via reaction with O2. Passive NO2-based systems use catalyzing agents to form NO2 from NO already present in the exhaust gas, typically in an oxidation catalyst upstream of the DPF, and to reduce the activation energy required for a NO2/soot reaction to occur at temperature levels achievable in some portion of the normal engine operation range without active thermal management of the reactants.
Many implementations of the active O2-based and passive NO2-based concepts for DPF regeneration have been demonstrated. The primary limitation of passive NO2-based regeneration is its inability to guarantee adequate regeneration of the DPF in all applications. To solve this, active O2-based regeneration is implemented alternatively to, or in addition to, passive NO2-based regeneration. The primary limitations of O2-based regenerations are lower maximum DPF soot loading levels, which must be observed, and a significantly higher temperature requirement than is necessary for NO2-based regeneration. The higher temperature requirement, as well as the need for more frequent regenerations, can lead to deterioration in the performance and durability of all affected exhaust aftertreatment devices, including those downstream of the soot filtration and regeneration components, such as an SCR system. Solution of the temperature problem must be resolved through the development of more robust aftertreatment devices and/or the implementation of additional devices, systems and/or methods to reduce post-DPF temperatures.
Some methods have been proposed that are supplemental to the active O2-based and passive NO2-based regenerations concepts. U.S. Patent Application Publication No. 2007/0234711 discusses a method to initiate an alternative control strategy with optimal NOx production during operating regimes where adequate reactant temperatures have been passively established. U.S. Pat. No. 6,910,329 B2 discusses a method whereby reactant temperatures and DPF volumetric flow (and thereby DPF residence time) are actively manipulated in order to extend the operating regimes where adequate passive NO2-based regeneration activity can be achieved.
In accordance with an aspect of the present invention, a method for regenerating a catalyzed diesel particulate filter (DPF) via active NO2-based regeneration with enhanced effective NO2 supply comprises introducing a NOx containing gas into the DPF, and controlling a temperature of at least one of the DPF, the NOx containing gas, and soot in the DPF while controlling NOx levels at an inlet of the DPF so that the NOx containing gas reacts with the catalyst to form NO2 molecules that thereafter react with soot particles to form CO, CO2, and NO molecules and a NO2 efficiency is greater than 0.52 gC/gNO2 and so that less than two thirds of the soot mass that is removed from the DPF is oxidized by O2 molecules in the gas to form CO and CO2 molecules.
In accordance with yet another aspect of the present invention, a diesel engine arrangement comprises a diesel engine arranged to introduce a NOx containing gas into a catalyzed diesel particulate filter (DPF), a heating arrangement arranged to control a temperature of at least one of the DPF, the NOx containing gas, and soot in the DPF, and a controller arranged to control the heating arrangement to perform an active NO2-based regeneration with enhanced effective NO2 supply by controlling the temperature and by controlling NOx levels at an inlet of the DPF so that the NOx containing gas reacts with the catalyst to form NO2 molecules that thereafter react with soot particles to form CO, CO2, and NO molecules and a NO2 efficiency is greater than 0.52 gC/gNO2 and so that less than two thirds of the soot mass that is removed from the DPF is oxidized by O2 molecules in the gas to form CO and CO2 molecules.
In accordance with yet another aspect of the present invention, a method of regenerating a diesel particulate filter (DPF) comprises performing a first regeneration to at least partially regenerate the DPF by performing an active NO2-based regeneration with enhanced effective NO2 supply, the active NO2-based regeneration with enchanced effective NO2 supply comprising introducing a NOx containing gas into the DPF, and controlling a temperature of at least one of the DPF, the NOx containing gas, and soot in the DPF while controlling NOx levels at an inlet of the DPF so that the NOx containing gas reacts with the catalyst to form NO2 molecules that thereafter react with soot particles to form CO, CO2, and NO molecules and a NO2 efficiency is greater than 0.52 gC/gNO2 and so that less than two thirds of the soot mass that is removed from the DPF is oxidized by O2 molecules in the gas to form CO and CO2 molecules, and performing a second regeneration to at least partially regenerate the DPF by performing at least one of a conventional NO2-based regeneration and an active O2-based regeneration.